The present invention relates to cutoff machines used in the continuous production of tubing. In general, tube and pipe mills employ a variety of cutoff machines, including press cut (single cutoff or double cutoff), rotary cutoff, metal saw cutoff, cutting tool cutoff, and plasma cutoff systems. The present invention relates primarily to press cutoff systems, which are used for high speed mills which produce medium and small diameter tubing.
U.S. Pat. No. 4,637,287, assigned to Kusakabe Electric and Machinery Co., Ltd., is an example of a cutoff device in which the present invention is applicable. The press cutoff machines shown in the '287 patent includes a rotatable press assembly, and a vertically actuated cutoff blade. The cutoff blade is carried by a die set which is accelerated horizontally into synchronous movement with the continuously produced tubing. When the die set has matched the velocity of the tubing being produced, the vertically actuated cutting blade is forced through the tubing to achieve the cutting operation. Once the cut has been made, the cutting blade is lifted and the die set is decelerated.
In the continuous production of tubing, the useful life of critical components, such as the cutoff cutting blade, is extremely important. In order to change a cutoff cutting blade, the entire tube manufacturing line must be stopped. Even in small diameter mills, the time required to change the cutting blade results in significant loss in productive time. Therefore, it is important to maximize to the fullest extent possible the useful life of cutoff cutting blades.
Cutting blade life can be lengthened if the temperature at which cuts are made is minimized. One technique for keeping the temperature of a cutting blade lower is to make cuts at a slower speed. The reduced cutting speed or longer cutting time results in fewer cutting blade replacements.
Traditionally, cutting stations in a tube producing mill were designed to use a cutting speed (vertical cutting blade velocity) which was merely sufficient to accomplish cutting of all sizes of tubes to be produced. No particular attention was paid to the speed of the cutting blade, and no attempts were made to vary it. By varying the speed of cutting in order to take advantage of the full stroke of the cutting assembly, the blade life is improved and the cutting force is better distributed over the press assembly.
Therefore, it is an object of the present invention to provide a cutoff machine which reduces the number of blade replacements.
Another object of the invention is to provide a cutoff machine which reduces the heat transferred to a cutting blade.
Still another object of the invention is to provide a cutoff machine which maximizes the time during which a cut is made.
Yet another object of the invention is to provide a cutoff machine which allows cuts to be made at lower temperature without sacrificing mill efficiency.
These and other objects of the invention are achieved with a cutoff machine which includes a frame with cutting and press assemblies coupled with each other. The cutting assembly is translatable to a velocity which matches that of the tubing to be cut. After the cutting assembly has reached a velocity which matches the tubing velocity, the press assembly causes the cutting blade to shear the tubing. In the device of the present invention, the speed at which the cutting blade passes through the tubing is determined in such a way as to fully maximize the translational stroke of the cutting assembly. This is accomplished by monitoring the tubing velocity and calculating a press assembly angular velocity which will cause completion of the cut at a point in time which takes full advantage of the time which is required in order to return the cutting assembly to a position from which a subsequent cut can be made.